The failure of immune tolerance is an important underpinning of all human autoimmune diseases. When tolerance fails, autoimmune processes damage vital organs in tens of millions of patients worldwide. The applicant will focus on this scientific challenge through fundamental investigation of the most common pediatric autoimmune disorder-Type 1 diabetes, which afflicts more than 2 million Americans. To prevent and reverse this disease, it is necessary to restore immune tolerance to islet antigens. The PI's K08 award has focused on the role of regulatory B lymphocytes in the induction and maintenance of immune tolerance. Because B lymphocyte development is directed primarily in the bone marrow, we have investigated the bone marrow response to tolerance induction. As described in the preliminary data, we have demonstrated that tolerogenic therapy induces mobilization of hematopoietic stem cells in tolerance-susceptible, non-autoimmune B6 mice but fails to do so in tolerance-resistant, diabetes-prone NOD mice. The mobilization of the bone marrow is dependent upon signals from the sympathetic nervous system that are activated by tolerogenic therapy with monoclonal antibody anti-CD45RB. In this proposal, we will determine the role of hematopoietic stem cell mobilization during tolerance induction, its control by bone marrow intrinsic and extrinsic factors, and the effect of the modulating influence of sympathetic input to the marrow. In aim 1, we will determine the cellular target of anti-CD45RB therapy that results in HSC mobilization, the mechanism of this effect, and its role in immune tolerance. In Aim 2, we will apply these findings to correct immune dysfunction and restore transplantation tolerance in NOD mice, the primary model of human Type 1 diabetes. Overall, these studies explore a new paradigm for the induction and maintenance of immune tolerance in which mobilization of stem cells in the bone marrow is needed to maintain homeostasis in the regulatory arm of the immune system. Breakdowns in this process may lead to erosion of tolerance over time and the resultant development of autoimmunity. This proposal will advance the independent studies of the PI to become a leading investigator focused on reprogramming of the immune system to achieve lasting immune tolerance for reversal of Type 1 diabetes.